Tint four cups of buttercream dark green and two cups of buttercream lighter green.
Use four cups of buttercream to fill and stack the cakes. Chill the stacked cakes.Take the chilled stacked cakes and using a serrated knife slice the front section of the 6 inch cake and 8 inch cake off on an angle creating a slope. Brush crumbs off cake. Ice the entire surface of the cakes with dark green buttercream. Do not smooth the icing out.
Roll out white fondant to approximately 1/8 of an inch. You want it long enough to flow down the side of your cake with a little extra for the pool at the top.
Use a sharp paring knife to cut out the outline of the river. There is no set template for this shape, just cut what will be visually appealing.
Lay the fondant on the cake down the sloped side pressing lightly into the icing.
Place the prepared trees on the cake. Put at least one tree on each level with a nice grouping on the very top around the pool. Set the larger rocks onto cake as well putting at least one in the middle of the waterfall for effect.
Fill disposable piping bag topped with a coupler and #234 decorating tip with light green icing .Use lighter green icing to make grass along the base and in bunchs on the various levels.
Continue to add elements to the cake on all levels until a rustic wild scene is created. Use both shades of green to provide nice contrast for the grasses surrounding the cake.
Squeeze the blue sparkle gel onto the fondant riverbed taking care to start from the top and fill in all the crannies created by the fondant rocks.
Allow the gel to trickle down like water on the slope of the falls smoothing with the palette knife to cover completely.
When the entire surface of the falls is covered with blue sparkle gel squeeze a little white gel where the middle rock is in the “water”. Also create foam at the bottom with the white sparkle gel. Use the paint brush to swirl the foam up realistically.
Squeeze blue decorating gel (darker) in lines down the falls and use the paintbrush to make darker water swirls.
Take the piping bag with darker green icing and pipe grasses along the entire waterfall to cover the exposed fondant edge. Optional: Pipe tiny white flowers in bunches with a closed star tip for contrast along the falls.